Syphilis is a sexually transmitted infection (STI) caused by the bacterium Treponema pallidum. The disease develops in distinct stages, starting with a characteristic sore where the bacteria entered the body. Recognizing this initial stage is important because the disease is highly contagious and can cause serious health complications if not treated early.
Characteristics of the Primary Syphilis Sore
The initial sign of syphilis is a small, firm, round ulcer known as a chancre, which develops at the site of infection. This sore usually appears between 10 and 90 days after exposure, with an average incubation period of about three weeks. The chancre is painless, which often causes it to go unnoticed, especially if hidden inside the vagina, rectum, or mouth.
A primary chancre is typically firm, clean, and non-bleeding. Bleeding generally occurs only if the sore is physically irritated, scraped, or located in a high-friction area. The bacteria-filled fluid oozing from the chancre is highly infectious and is usually clear or slightly serous rather than bloody.
The chancre typically heals on its own within three to six weeks, even without treatment. This spontaneous healing often misleads an infected person into thinking the infection is gone, but the bacteria remain active. This initial sore represents the most contagious stage, making early recognition and treatment important for preventing transmission.
How Syphilis Progresses If Left Untreated
Once the primary chancre heals, the infection moves into the secondary stage a few weeks later. During this phase, the bacteria spread throughout the bloodstream, causing systemic symptoms. The most common sign is a non-itchy, reddish-brown rash that can appear anywhere on the body, frequently involving the palms and soles of the feet.
Other secondary symptoms may include flu-like signs such as fever, sore throat, fatigue, and swollen lymph nodes. Moist, wart-like patches, called condylomata lata, can sometimes appear in the genital or anal areas. These symptoms may come and go for up to two years, but they eventually resolve on their own, even without medical intervention.
The disease then enters the latent stage, where there are no visible signs or symptoms, but the infection remains present. This hidden stage can last for years or decades. It is categorized as early or late latent syphilis depending on whether the infection occurred within the past year. Without treatment, approximately one-third of people in the latent stage will progress to the late, or tertiary, stage.
Tertiary syphilis is the most serious phase, occurring 10 to 30 years after the initial infection, causing severe damage to internal organs. This stage can affect the heart and blood vessels, leading to cardiovascular issues, or the brain and nervous system, resulting in neurosyphilis. Potential complications include loss of coordination, paralysis, blindness, dementia, and death.
Testing and Treatment Options
Diagnosis of syphilis begins with a physical examination of any suspicious sores, but confirmation requires specific laboratory tests. The most common diagnostic method involves blood tests, such as the Rapid Plasma Reagin (RPR) or Venereal Disease Research Laboratory (VDRL) tests, which look for antibodies the body produces. If a primary chancre is present, fluid from the sore can also be examined under a dark-field microscope to directly identify the Treponema pallidum bacteria.
The preferred and most effective treatment for all stages of syphilis is the antibiotic Penicillin G. For primary, secondary, and early latent syphilis, a single intramuscular injection of long-acting Benzathine Penicillin G is typically sufficient. The bacterium is highly sensitive to penicillin, making this a reliable cure when administered early.
Treatment for late latent or tertiary syphilis requires a longer course, usually three separate injections of Penicillin G given at weekly intervals. Patients with neurosyphilis, where the infection has reached the brain or spinal cord, require high doses of intravenous Penicillin G for 10 to 14 days. Alternative antibiotics, such as doxycycline or tetracycline, are available for those with a penicillin allergy, though penicillin is the only recommended treatment for pregnant individuals.
After treatment, follow-up blood tests are necessary to ensure the infection has been eradicated and antibody levels have decreased. Individuals diagnosed with syphilis must notify their sexual partners so they can be tested and treated, preventing further spread. Treatment of a sexual partner is often recommended presumptively if they were exposed within the preceding 90 days, even before their test results are available.